ABSTRACT
The mechanisms occurring on a micro-scale at sand-pile interface during axial displacement controlled cyclic loading were analysed quantitatively using x-ray tomography and a grain-based approach of three dimensional digital image correlation. The tests were performed in a mini-calibration chamber using a range of values of cyclic amplitudes and number of cycles. The results were found to be consistent with those obtained in a previous study carried out in a large calibration chamber, at Laboratoire 3SR, in France. The macroscopic response of sand-pile interface showed a two-regime evolution during cycles, with a non-negligible increase of shaft resistance in the latter regime. The test conditions are not representative of real engineering applications, where piles supporting bridges, tidal or wind turbines have to safely sustain severe load-controlled cycles. However, advanced image analysis sheds light on the mechanisms controlling the macroscopic behaviour of the sand-pile interface in each regime.
